Pulsed droplet ejecting system

ABSTRACT

An electro-acoustic transducer is coupled to liquid in a conduit which terminates in a small orifice. Preferably, the acoustic impedance of the supply portion of the conduit is large compared with the acoustic impedance of the orifice. The liquid is under small or zero static pressure. Surface tension at the orifice prevents liquid flow when the transducer is not actuated. An electrical pulse with short rise time causes sudden volume change at the transducer, thereby creating an acoustic pressure pulse having sufficient amplitude to overcome the surface tension at the orifice and eject a small quantity of liquid therefrom. The expelled liquid is replaced by forward flow of liquid in the conduit under the influence of capillary forces in the orifice.

United States Patent Zoltan [54] PULSED DROPLET EJECTING SYSTEM [72]Inventor: Steven I. Zoltan, Shaker Heights,

Ohio

[73] Assignee: Clevite Corporation [22] Filed: Sept. 9, 1970 [21] Appl.No.: 70,838

[52] U.S. Cl ..3l0/8.3, 259/DIG. 44, 310/8, 310/8.l, 310/8.5, 3l0/9.1,310/9.6, 346/75,

[51] Int. Cl ..H0lv 7/00, H04r 17/00 [58] Field of Search ..3l0/8-8.3,8.5, 310/8.6, 8.7, 9.1, 9.4, 9.6; 259/1 R, DIG. 41,

DIG. 44; 417/322; 346/75, 140

[ 1 Aug. 8, 1972 I OTHER PUBLICATIONS Ultrasonics-October 1967, pp. 214-218, Article by E. G. Lierke entitled Ultrasonic Alomizer Incorporatinga Self-Acting Liquid Supply.

Primary Examiner-J. D. Miller Assistant ExaminerMark O. BuddAttorney-Eber J. Hyde [57] ABSTRACT An electro-acoustic transducer iscoupled to liquid in a conduit which terminates in a small orifice.Preferably, the acoustic impedance of the supply portion of the conduitis large compared with the acoustic impedance of the orifice. The liquidis under small or zero static pressure. Surface tension at the orificeprevents liquid flow when the transducer is not actuated. An electricalpulse with short rise time causes sudden volume change at thetransducer, thereby creating an acoustic pressure pulse havingsufficient amplitude to overcome the surface tension at the orifice andeject a small quantity of liquid therefrom. The expelled liquid isreplaced by forward flow of liquid in the conduit under the influence ofcapillary forces in the orifice.

6 Claims, 10 Drawing Figures PAIENTEDAus 8 m2 sum 2 0r '3 FIG.2b

FIG.3

INVENTOR. STEVEN l. ZOLTAN FIG.4

ATTORNEY STEVEN I. ZOLTAN ATTORNEY 1 PULSED DROPLET EJECTING SYSTEMBACKGROUND OF THE INVENTION developed which employ a stream of inkdroplets. The 1 ink under static pressure is expelled through a smallorifice. The emerging stream of ink breaks up into droplets which tendto be of non-uniform size and spacing. It has been found that ultrasonicvibrations of suitable frequency applied to the nozzle or to the inksupply tend to regularize the spacing and size of the droplets. In someapplications, such as character printers and facsimile recorders, it isnecessary to prevent, controllably, some of the droplets from reachingthe record medium. In U.S. Pat. No. 3,298,030 to Lewis and Brown, theunwanted droplets are deflected electrostatically away from the recordmedium into an ink dump. In U.S. Pat. No. 3,416,153 to Hertz et al, theink jet is propelled through an opening in a shield to the recordmedium. When droplets are not wanted, the stream is dispersed by anelectric field so that it is intercepted by the shield. These methods ofdroplet generation and control are relatively complicated and expensive.Streams of ink droplets may be developed without employing staticpressure. In U.S. Pat. No. 2,512,743 to Hansell, a piezoelectricultrasonic transducer vibrates at a mechanical resonance frequency ofthe transducer. The pressure to eject the droplets is said to resultfrom cavitation in the ink, with the quantity of ink expelled beingcontrolled by modulating the ultrasonic power source.

In U.S. Pat. No. 3,452,360 to Williamson, a magnetostrictive transducerrod vibrates at a frequency well above the fundamental length moderesonance of the rod, presumably at a length mode overtone. One end ofthe vibrating rod is coupled to the ink adjacent to a flexible nozzle.The flexibility of the nozzle and a non-circular orifice provide a checkvalve action so that ink is expelled during each expansion stroke of therod. The ink stream may be modulated by modulating the high frequencypower source which drives the transducer.

SUMMARY OF THE INVENTION The principal object of this invention is toprovide a system which ejects a small quantity of liquid only uponelectrical command.

Another object is to provide such a system which does not require apressurized liquid supply.

Another object is to provide a system which ejects liquid uponelectrical command, the quantity at each command being controllable.

According to the invention a reservoir supplies liquid through a conduitto an orifice which has acoustic impedance. A supply portion of theconduit, which communicates with the reservoir, is adapted for flow ofliquid in both directions and has acoustic impedance at least as high asthe acoustic impedance of the orifice. The conduit has a second portionlocated between the supply portion and the orifice. Means are providedfor causing a droplet to be expelled from the orifice upon commandcomprising an electroacoustic transducer coupled to the liquid in thesecond portion of the conduit, and means for applying an electricalpulse to the transducer each time it is desired to have a dropletexpelled from the orifice.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a system according to theinvention partly in section and partl schematic. 0 3

FIG. 1a shows a modification of the system of FIG. 1.

FIG. lb shows another modification of the system of FIG. 1.

FIG. 2 shows one of many alternate circuit arrangements suitable for usein this invention.

FIG. 1a shows a modification of the circuit of FIG. 2.

FIG. 2b shows another modification of the circuit of FIG. 2.

FIG. 3 shows another suitable circuit arrangement.

FIG. 4 is a partial, sectional view illustrating a modifiedtransducer-orifice arrangement.

FIG. 5 shows another transducer-orifice arrangement.

FIG. 6 is a sectional view of still another transducerorificearrangement.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, areservoir shown schematically at 1 contains ink or other liquid 2. Aconduit indicated generally be reference characters 4 communicates withliquid 2 in the reservoir and is filled with the liquid. A small orifice5 in conduit 4 is provided for exit of liquid, shown as droplets 7.

Conduit 4 comprises a length of small bore tubing 8, electroacoustictransducer 10, and orifice plate 11. Tube 8 may extend to the reservoir,or, as shown, conduit 4 may include a larger diameter portion 6, such asplastic tubing, connecting tube 8 with the reservoir.

Transducer 10 comprises a length of small diameter piezoelectric ceramictubing 13. The diameter may, for example, be about 0.05 inch. Tube 13 isprovided with electrode 14 on the inner surface and electrode 16 on theouter surface. The electrodes, as shown, do not extend to the ends oftube 13, but full length electrodes may be employed if desired. Tube 13is polarized radially.

A thin wire 17 is wrapped around tube 13 in contact with outer electrode16 and soldered thereto, as shown at 19. Wire 17 thus serves as oneelectrical terminal of the transducer.

Tube 8, made of any suitable metal, such as copper or stainless steel,is cemented into the end of ceramic tube 13 by means of conductive epoxy9 which contacts inner electrode 14. Thus, tube 8 serves as the secondelectrical terminal for the transducer.

For orifice plate 11, it is convenient to use a jewel watch bearing.Such jewels are readily available at low cost and have accuratelycontrolled dimensions in the range suitable for the present use. Orifice5 may, for example, have diameter and length on the order of 0.06millimeter. Jewel 11 may be attached to the end of transducer 10 bymeans of an epoxy adhesive 12.

Transducer 10 operates by virtue of the wellknown piezoelectric effect.When a d-c voltage is applied between the electrodes the length and theinside diameter of the tube both increase or decrease slightly, de-

pending on the polarity in relation to the polarity of the polarizingd-c voltage used during manufacture. The response is nearlyinstantaneous, being retarded very slightly by inertia reaction.

When it is-desired to have a small quantity of liquid expelled fromorifice 5, a short rise time voltage pulse is applied to the transducerat terminals 8 and 17, the polarity being selected to cause contractionof the transducer. The resulting sudden decrease in the enclosed volumecauses a small amount of liquid to be expelled from orifice 5. Someliquid also is forced by the pressure pulse back into tube 8, but theamount is relatively small, due to the high acoustic impedance createdby the length and small bore of the tube.

From the foregoing, it may be seen that the system of this inventionejects a small quantity of liquid on command. The command signal is theshort rise time pulse.

-By means of simple circuitry, command pulses may be supplied to causeejection of a succession of small quantities of liquid according to anydesired time pattern, limited only by the maximum response speed of thesystem. In FIG. I a train of command pulses corresponding to exitingdroplets 7 is illustrated at 22.

Static pressure on the liquid is not required. However, small positiveor negative pressure does not interfere with operation, the chiefrequirement being that such static pressure alone must not be greatenough to overcome the surface tension of the liquid at orificeotherwise liquid may run out, or air may enter the system underquiescent conditions.

When the actuating electrical pulses have energy below the levelrequired to overcome the surface tension at the orifice, droplets arenot expelled, but under stroboscopic illuminationthe liquid can beobserved bulging out of the orifice momentarily during each pulse. Atsomewhat higher drive energy levels, well developed single droplets areexpelled, one for each pulse. At still higher energy levels, additionalliquid is expelled in the form of additional, separate droplets, or thetotal amount of liquid expelled at each drive pulse may take the form oflong cylinders of liquid with rounded ends. Thus, the quantity of liquidexpelled at each pulse can be controlled by controlling the energy inthe driving pulse. This enables use of the invention in recordersrequired to print with controlled shading, i.e., with gray scale,without the necessity of producing multiple ink spots per pictureelement.

Considerable latitude is available in the design of systems according tothis invention. The interacting design variables are numerous and, asyet, a mathematical design technique has not been developed. However,the following guide lines and example should enable those skilled inelectroacoustics to arrive at a satisfactory design.

To avoid wasting an excessive part of each transducer pulse in drivingliquid from the transducer toward the reservoir, it is desirable to haverelatively high acoustic impedance looking from the transducer into thesupply portion of the conduit, as provided by small bore tube 8 inFIG. 1. However, this is not a requirement. Satisfactory performance maybe obtained without providing any constriction in the conduit. Asuitable arrangement is shown in FIG. la.

In FIG. la, liquid from a reservoir, not shown, is supplied totransducer 10' by plastic hose 6' which is forced over the end of thetransducer. Electrical connection to the inner electrode 14 is providedby extending the electrode over the end of ceramic tube 13 to the outersurface, as shown at 14'. Thin wire conductor 17' is secured toelectrode extension 14' by solder 19' and acts as a terminal for thetransducer. With this arrangement, somewhat higher amplitude electricalpulses are required to expel liquid.

FIG. lb shows a modification of the construction of FIG. la in which thesupply line acoustic impedance is made at least as high as the impedanceof the exit orifice, not including the efiect of surface tension at theorifice. The modification consists in cementing to the inlet end of thetransducer 10' a jewel 1 1 having opening 5' with the same dimensions asexit orifice 5.

Although the arrangements of FIGS. 1a and lb are satisfactory, generallyit is desirable to provide higher acoustic impedance at the transducerinlet. In the construction of FIG. 1, this is accomplished by use ofsmall bore tube 8. Other alternatives include a thin slit, or a porousmember, or other acoustic resistance, at the transducer inlet throughwhich the liquid must pass. Furthermore, some advantage would accruewhen using a tube such as 8 in FIG. 1, by adding an acoustic resistanceat the inlet end dimensioned to act as a matched acoustic terminationfor the tube as a transmission line. This would reduce, or eliminate,acoustic resonance effects in tube 8. However, excellent results havebeen obtained without such termination.

The change in volume within transducer 10, when the latter is pulsed,must exceed the volume of liquid to be ejected at orifice 5. The ceramiccomposition and the dimensions of tube 13 and the energy of theactuating pulses are factors that may be traded in arriving at asuitable design. Good results have been attained with transducer volumechange calculated to be about four times the volume of the liquid to beexpelled. For a fully electroded thin wall tube, unrestrained by endclamping or acoustic load, the fractional volume change due to thepiezoelectric effect is approximately:

where (AV/ V) volume change per unit volume d piezoelectric strainconstant E applied voltage t= thickness of tube wall Care must be takento measure wall thickness t in units consistent with the units used inexpressing (1 usually MKS units. THe negative sign indicates contractionwhen the applied voltage has the same polarity as the originalpolarizing voltage.

Another requirement is that the rate of change of volume must besufficient in relation to the acoustic impedance loading the transducerto develop enough pressure to overcome the surface tension at orifice 5.

A variety of simple circuits may be used to apply suitable commandpulses to the transducer. FIG. 2 shows one example in which thecapacitance of the transducer is used as part of the pulse shapingcircuit. In FIG. 2, transducer 10 is shown schematically in crosssection. The encircled polarity signs indicate that the ceramic tubeemployed in this example was polarized during manufacture with the innerelectrode positive, and the outer electrode negative. A d-c supply 20,shown for simplicity as a battery, has the negative terminal connectedto the inner electrode 14. The positive tenninal of supply 20 isconnected through series resistors 23, 25 to the outer electrode 16.Resistor 23 has a relatively high resistance and resistor 25 has arelatively low resistance.

Transistor 26 is used as a switch. Collector 32 is connected to thejunction between resistors 23 and 25, and the emitter 34 is connected tothe negative side of supply 20. Control pulses 31 may be applied betweenbase 28 and emitter 34 via terminals 29.

Under quiescent conditions, the switch is open and the transducercapacitance is charged to the voltage of supply 20. Since the polarityof the applied voltage is the opposite of the original polarizingpolarity, the transducer is in an expanded state.

When a pulse 31 is applied to terminals 29, transistor 26 switches to alow value of collector-emitter resistance for the duration of the pulse.This permits the capacitance of the transducer to discharge rapidlythrough low resistance 25 and the transistor ON resistance. Thetransducer responds by contracting suddenly, expelling a small quantityof liquid at orifice S, as previously described.

When pulse 31 falls approximately to zero, transistor 26 turns off,allowing the transducer capacitance to recharge through resistors 23, 25to the voltage of supply 20. Due to the higher value of resistor 23, thecharging takes place relatively slowly. The transducer responds byexpanding slowly, while liquid from tube 8 replaces the liquid expelled,as previously described. Thus, in response to control pulses 31, thecircuit provides short rise time command pulses having relatively longdecay times, as shown at 33. For best results, the decay time should beat least four times the rise time.

Some improvement in performance is obtained by adding an inductance 36in series with the collector of the transistor, as shown in FIG. 2a, orin series with the transducer, as shown in FIG. 2b.

For a transducer having capacitance of about 5,000 picofarads aninductance in the range of l to millihenries has given good results. Atypical wave form for the pulse voltage applied to the transducer isshown at 33.

An example of a satisfactory system design is summarized in thefollowing table, referring to the construction of FIG. 1:

Ceramic tube 13 Length 12.7 millimeters lnside diameter .76 millimetersWall thickness .25 millimeters Composition lead zirconate-lead titanatetype having the following published nominal Liquid Water base ink havingviscosity and surface tension similar to water Drive circuit FIG. 2b

Supply 50 volts Transistor 26 M1 421 Resistor 25 200 ohms Resistor 231000 ohms Inductor 36 2 millihenries Control pulse 31 Amplitude 3milliamperes Duration 20 microseconds Droplets Diameter of ink spot .13millimeter Exit velocity 1 to 2 meter/second Repetition rate up to50,000/second For definitions of the characteristics listed for theceramic material, reference may be made to: lRE Standards ofPiezoelectric Crystals Measurements of Piezoelectric Ceramics.Proceedings of the [RE Vol. 49, No. 7,July 1961 (IEEE 179l961).

With the circuit of FIG. 2 there is a limit to the supply voltage 20beyond which depolarization of the ceramic may result. The limit dependson the composition of the ceramic material and on the wall thickness oftube 13. FIG. 3 illustrates a circuit arrangement that does not havethese limitations but requires additional components.

In FIG. 3 the positive terminal of supply 20 is connected to the innerelectrode 14 of transducer 10 and the negative terminal is connectedthrough transistor switch 26 and resistor 25 to outer electrode 16. Whenthe transistor is off, no voltage appears at the transducer. When thetransistor is on, the voltage of supply 20 is applied to the transducerwith the same polarity used during polarization of the ceramic tube,thus, depolarization due to the excessive voltage cannot take place.Blocking capacitor 35 couples the control pulses applied at terminals 29to the transistor base 28. Diode 37 permits the normal quiescent chargeto be reestablished at capacitor 35 as the control pulse falls to zero.

Under quiescent conditions transistor 26 is turned off and, therefore,transducer 10 has no charge. When a control pulse 31 occurs, transistor26 turns on and the capacitance of transducer 10 charges rapidly throughlow resistance 25 and the ON resistance of the transistor. This requiresa low impedance supply at 20. The transducer responds by contractingrapidly, expelling liquid through the orifice. As pulse 31 falls tozero, transistor 26 is turned off and the capacitance of the transducerdischarges relatively slowly through large resistance 23. The transducerresponds by expanding slowly while the expelled liquid is replaced. Aninductance may be connected in series with the transistor or transduceras in FIGS. 20 or 2b.

1f the liquid is corrosive to the electrode material of the ceramictube, the construction of FIG. 4 may be employed. In this case, thesmall bore liquid supply tube 38 extends through transducer tube 13. Itis shown necked down at the end to form nozzle shaped orifice 39.However, a watch jewel, such as 11 in FIG. 1, or other orificearrangement may be used. Transducer tube 13 surrounding the conduit isin stress transmitting engagement with the wall of the conduit by virtueof epoxy cement 40 and, therefore, the transducer is coupled to theliquid within the conduit. This arrangement results in reducedsensitivity because of the stiffness of conduit tube 38, and, therefore,higher pulse energy is required to expel liquid and it is advantageousto use a circuit such as shown in FIG. 3.

It is not necessary that the liquid flow through the transducer. Forexample, in FIG. 5, conduit 42 comprises small bore supply section 8enlarged at the end thereof for attachment of orifice plate 11. A Textension 41 couples to one end of transducer 10. The other end oftransducer 10 is closed by cap 43. When a command pulse is applied, thetransducer contracts suddenly, expelling liquid from the transducer intoconduit 42. The resulting acoustic pressure pulse overcomes surfacetension at orifice 5, causing ejection of liquid such as droplet 7. Thehigh acoustic impedance of supply portion 8' retards flow back towardthe reser- VOll'.

This invention is not limited to the use of tubular piezoelectrictransducers. Different geometries and constructions may be used, as wellas different transducer principles. One variation is to replacepiezoelectric ceramic tube 13 of FIGS. 1,4, 5 with a tube formed from anelectrostrictive material having little or no remanent polarization. Inthis case, a pulse of either polarity will cause the same volumecontraction, and a circuit such as shown in FIG. 3 would be used.

Magnetostrictive transducers also may be employed. One way to do this isto use magnetostrictive material in forming tube 38 of FIG. 4.Transducer tube 13 then is replaced by an energizing windingmagnetically coupled to the tube. To eject liquid, a short rise timecurrent pulse is applied to the winding.

As another example, FIG. 6 shows a sectional view of atransducer-conduit assembly employing a thin piezoelectric ceramic disc44. It is clamped around the periphery between O-ring gaskets 46, 47within a housing made up of members 49, 50. A small cross sectionannular passageway 51 is formed around the disc by the inner walls ofbody members 49, 50, O-rings 46, 47, and the exposed edge of disc 44. Asmall bore liquid supply tube 8 is secured in opening 52in body member50. The opening communicates with annular passageway 51. Tube 8 mayextend to a liquid reservoir or may be coupled thereto by larger tube 6.A second opening 54 also communicates with annular passageway 51 andterminates at orifice plate 11. Thus, a liquid conduit is formed bysupply tubes 6 and 8, opening 52, two parallel portions of annularpassageway 51, opening 54, and orifice plate 11.

Ceramic disc 44, exposed to the liquid only at the rim, acts as anelectroacoustic transducer coupled to the liquid. Flexible lead wires55, 56 are soldered to the electrodes 58, 59 of disc 44 and act asterminals for the transducer.

When it is desired to expel liquid from orifice 5 a short rise timevoltage pulse is applied to terminal wires 55, 56. This results insudden expansion of the diameter of transducer 44, displacing liquidfrom annular passageway 51. The resulting acoustic pressure pulse expelsliquid from orifice 5. As the pulse slowly goes to zero, liquid ispulled into annular passageway 51 from tube 8 to replace the liquidpreviously expelled.

Although many different circuit arrangements may be constructed to drivetransducer 44, it is convenient to use a circuit similar to the circuitof FIG. 2. In this case, however, the negative side of supply 20 isconnected to the electrode of transducer 44 that was negative duringpolarization. With this polarity, the quiescent voltage applied totransducer 44 holds the disc in diameter contracted condition. Whentransistor 26 is turned on by a pulse at terminals 29 the capacitance ofthe transducer discharges rapidly through the transistor and lowresistance 25. The transducer responds by expanding suddenly to thediameter it had prior to connection of power supply 20 and expelsliquid, as previously described. When the control pulse falls to zero,the transducer recharges to the voltage of supply 20, contracting indiameter as it does so.

While there have been described what are at present considered to be thepreferred embodiments of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is aimed,therefore, in the appended claims to cover all such changes andmodifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A system adapted upon pulsing to expel a small quantity or asuccession of small quantities of liquid in controlled manner,comprising:

a reservoir containing said liquid;

a conduit connected to said reservoir and communicating with the liquidtherein and filled with said liquid under low or zero static pressure,said conduit having an exit orifice which is sufficiently small thatsurface tension in the absence of pulsing prevents said liquid fromflowing therefrom;

a tubular transducer of given diameter surrounding said conduit instress transmitting engagement therewith and thereby coupled to theliquid therein adjacent said orifice, said transducer being adapted tocontract radially to displace a small quantity of said liquid overcomingsaid surface tension to expel a small quantity of said liquid throughsaid orifice and to expand to said given diameter prior to a subsequentcontraction;

electrical circuit means connected to said transducer for applyingthereto an electrical pulse of a given polarity and with short rise timeto cause said transducer to contract rapidly, and upon decay of saidpulse to allow said transducer to expand;

said conduit during operation of said system at all times being openfrom said reservoir to said orifice whereby the liquid within saidtransducer is replaced by liquid from said reservoir to make up for saidexpelled liquid upon said termination of said pulse.

2. A system as described in claim 1 in which the transducer is apiezoelectric transducer.

3. A system as described in claim 1 in which the transducer comprises atubular piezoelectric member which changes internal volume in responseto an electrical signal, said tubular member surrounding said secondportion of said conduit in stress transmitting engagement therewith.

4. A system as described in claim 1 in which the transducer is anelectrostrictive transducer.

5. A system as described in claim 1 in which the transducer is amagnetostrictive transducer.

6. A system as described in claim 1 wherein said means for applying anelectrical pulse includes means for adjusting the energy of said pulseaccording to the quantity of liquid that is desired to be expelledduring said pulse.

1. A system adapted upon pulsing to expel a small quantity or asuccession of small quantities of liquid in controlled manner,comprising: a reservoir containing said liquid; a conduit connected tosaid reservoir and communicating with the liquid therein and filled withsaid liquid under low or zero static pressure, said conduit having anexit orifice which is sufficiently small that surface tension in theabsence of pulsing prevents said liquid from flowing therefrom; atubular transducer of given diameter surrounding said conduit in stresstransmitting engagement therewith and thereby coupled to the liquidtherein adjacent said orifice, said transducer being adapted to contractradially to displace a small quantity of said liquid overcoming saidsurface tension to expel a small quantity of said liquid through saidorifice and to expand to said given diameter prior to a subsequentcontraction; electrical circuit means connected to said transducer forapplying thereto an electrical pulse of a given polarity and with shortrise time to cause said transducer to contract rapidly, and upon decayof said pulse to allow said transducer to expand; said conduit duringoperation of said system at all times being open from said reservoir tosaid orifice whereby the liquid within said transducer is replaced byliquid from said reservoir to make up for said expelled liquid upon saidtermination of said pulse.
 2. A system as described in claim 1 in whichthe transducer is a piezoelectric transducer.
 3. A system as describedin claim 1 in which the transducer comprises a tubular piezoelectricmember which changes internal volume in response to an electricalsignal, said tubular member surrounding said second portion of saidconduit in stress transmitting engagement therewith.
 4. A system asdescribed in claim 1 in which the transducer is an electrostrictivetransducer.
 5. A system as described in claim 1 in which the tRansduceris a magnetostrictive transducer.
 6. A system as described in claim 1wherein said means for applying an electrical pulse includes means foradjusting the energy of said pulse according to the quantity of liquidthat is desired to be expelled during said pulse.